This volume tracks the impact Processing Instruction has made since its conception. The authors explain Processing Instruction, both its main theoretical underpinnings as well as the guidelines for developing structured input practices. They review the empirical research conducted to date, so that readers have an overview of new research carried out on the effects of Processing Instruction. The work concludes with reflections on the generalizability and limits of the research on Processing Instruction and offers future directions for Processing Instruction research.